False alarms are a challenging issue for an intrusion detection system (IDS), which can significantly decrease the effectiveness of detection and heavily increase the burden on analyzing true alarms. With the advent of cloud computing, it is a big chance to mitigate this problem in such a promising environment. In our previous work, we proposed to construct an intelligent false alarm filter by selecting an appropriate algorithm in an adaptive way, whereas the additional workload may be an issue for implementation. In this paper, we begin by presenting a Generic Cloud-based Intrusion Detection Architecture (GCIDA) and we then propose a cloud-based solution to improve the false alarm reduction and reduce the workload using Cloud as a Service (CaaS). In addition, we also describe the procedures and the interactions between the Cloud nodes and the Cloud providers. Experimental results indicate that CaaS can provide sufficient computing power and greatly reduce the workload of adaptive false alarm reduction.